An orthogonal down mixer (orthogonal demodulator) is typically used in a reception device of a cellular telephone or the like. The orthogonal down mixer has two mixer circuits. A local signal is applied to each mixer circuit, and the two mixer circuits respectively convert high frequency reception signals into low frequency signals (an I signal and a Q signal) and output the low frequency signals.
Further, an image elimination type reception device (employing a heterodyne system) outputs two low frequency signals following conversion into intermediate frequency signals by the orthogonal down mixer.
In this type of orthogonal down mixer or the like, the phases of the two output signals preferably deviates by 90°, and for this purpose, the phases of the two local signals applied to the mixer circuits of the orthogonal down mixer preferably also deviates by precisely 90°.
However, the frequency of the local signals applied to the respective mixer circuits is high, and it is therefore difficult to cause the phase to deviate by precisely 90°.
Hence, an image elimination type receiver and an orthogonal modulator formed to be capable of correcting a phase error are known in the prior art (Japanese Patent No. 3,398,910 and Japanese Laid-open Patent Publication No. 2002-232497, for example).
However, in the image elimination type receiver discussed in Japanese Patent No. 3,398,910, the high frequency local signal applied to one of the mixers is adjusted, and therefore the precision with the phase difference between the local signals is shifted to 90° is poor. Further, a circuit for adjusting the phase handles the high frequency local signals, and therefore the overall power consumption of the receiver is large. Moreover, a control circuit and a plurality of phase adjustment circuits are provided, and therefore the circuit area of the receiver is large.
Further, in the orthogonal modulator discussed in Japanese Laid-open Patent Publication No. 2002-232497, analog calculation processing is performed on the two low frequency signals (the I signal and the Q signal), and therefore an active element is employed, leading to increases in the overall circuit area and power consumption of the orthogonal modulator. Moreover, it is difficult to execute analog calculations at a high frequency, and therefore, although this technique can be applied in principle to an orthogonal modulator in which the orthogonal signals have a low frequency, it cannot be used in a receiver in which the orthogonal signals have a high frequency.